Predicting off‐site impacts on breeding success of the marsh harrier

Abstract

Construction of buildings, and other types of land uses by humans can exert negative impacts on wildlife that live in the areas surrounding such developments (i.e., off‐site impacts). To reduce or lessen such impacts, it is important to determine the biological metrics (e.g., abundance, breeding success) that are affected and at which spatial scales. We monitored the eastern marsh harrier (Circus spilonotus) breeding in wetland patches in northern Japan for 4 years and quantified its abundance (no. pairs) and breeding success (no. juveniles) in natural environments compared to artificial land uses in the surrounding areas. We developed a hierarchical model to simultaneously infer the effects of foraging habitats and artificial land uses on the numbers of pairs and juveniles. We found that the amount of foraging habitat within 0.5 km of wetland patches positively influenced the number of pairs per patch and that the amount of artificial land use within 2.0 km from the patches negatively influenced the number of pairs per patch and the number of juveniles per pair. The number of juveniles per patch was therefore affected by these 2 features and was most susceptible to increased land use by humans within 2.0 km from the patches. Our results can be used to predict the magnitudes of off‐site impacts on eastern marsh harriers before any additional development occurs. To effectively manage off‐site impacts, we highlight the importance of considering species abundance and the biological processes mediating breeding success that are possibly affected by different land uses. © 2017 The Wildlife Society.